There is evidence showing that aluminum from the environment has access to and is stored in human tissues. The neurotoxicity of aluminum has been demonstrated by clinical and experimental studies. High concentrations of aluminum have been found in the brain tissue of elderly people and of patients affected with Alzheimer's Disease. In Alzheimer's disease and in parkinsonism-dementia of Guam, neurons, that have accumulated tangles of paired helical filaments, contain high levels of aluminum. Furthermore the lumbar motoneurons in amyotrophic lateral sclerosis contain relatively high levels of aluminum. In spite of this evidence the specific role of this metal in the pathogenesis of the neuronal alterations and losses observed in these diseases is still undetermined. The evolution of the cellular changes in neurons exposed to prolonged aluminum intoxication has not been determined in experimental conditions. A chronic experimental model is therefore necessary. Such an experimental model of neurological disease has been obtained by injecting metallic aluminum powder into the cerebrospinal fluid of rabbits. The animals develop a slowly progressing encephalomyelopathy characterized by the early appearance of neurofibrillary tangles of 10nm filaments and later by the presence of neuronophagias in several areas of gray matter. In the late phase of the disease severe weakness is observed and the muscle shows evidence of neurogenic atrophy. In order to test the hypothesis as to whether aluminum indeed induces neuronal losses in areas of the central nervous system, we propose to conduct morphometric studies of the anterior horn of the cervical spinal cord and of the anterior roots of rabbits injected with aluminum, compared to controls. Histochemical studies of the muscle will also be performed. The demonstration of neuronal losses accompanied by loss of axons in the anterior roots and in the peripheral nerve, and the presence of neurogenic atrophy of the striated muscle will be considered strong evidence of a deleterious and irreversible effect of aluminum upon nerve cells.